Export FBX to Unreal
It all depends on your game. although unreal is good at handling high poly assets if you do LOD.
The smoothing option is for smooth shading.

My recommendation would be to make range of tris budget count for assets (like up to 2k tris for none important and up to 12k tris for important, although if its a vr game you can go higher it's up to you and your target hardware and frame rate)